Winglet

ABSTRACT

A winglet ( 12 ) for an aircraft wing is provided. The winglet ( 12 ) has an airflow control arrangement, for example in the form of a trailing edge flap ( 20 ) by means of which lift generated by the winglet can be varied. The control arrangement desirably forms part of a manoeuvre load alleviation system ( 22 ) for the aircraft.

[0001] The invention relates to a winglet.

[0002] A winglet generally takes the form of an upturned tip on a wingor other flying surface on an aircraft although the term “winglet” mayalso embrace an end plate which extends both above and below the upperand lower surfaces at the tip of a wing or other flying surface.

[0003] The presence of a winglet serves to increase the efficiency of awing by reducing drag which would otherwise be induced by wing tipvortices. At the same time, the presence of the winglet increasesloading on the wing by virtue of increased lift in the tip region of thewing during flight. The increased lift resulting from the winglet alsocreates a side force towards the root of the wing which creates anadditional bending moment about the root. The consequence of these loadincreases is that the wing structure has to be made stronger whichresults in an increase in weight. Therefore whilst increasing efficiencyon the one hand, there are, on the other hand, effects which areundesirable and particularly so when the aircraft undergoes high gmanoeuvres which is a design load case for some areas of the wing.

[0004] An object of the present invention is to provide a winglet inwhich the foregoing undesirable effects are reduced whilst stillmaintaining the advantages of the winglet as far as wing efficiency isconcerned.

[0005] According to a first aspect of the invention there is provided awinglet for an aircraft wing, the winglet having a control arrangementthereon by means of which lift generated by the winglet can be varied.

[0006] By providing the control arrangement, the lift generated can bereduced during manoeuvring so as to reduce the loading which wouldotherwise be generated on the wing and thereby provide manoeuvre loadalleviation (MLA). In the normal cruise condition the control system isnot activated and hence the presence of the winglet serves to minimisethe effect of wing tip vortices thereby still serving to improveefficiency of the wing.

[0007] The control arrangement may be an active control arrangementlinked to a control system of the aircraft, for example, as part of aMLA system if present, or it may be a passive control arrangement whichwould automatically operate in response to a predetermined loadcondition.

[0008] In the active control case, the control arrangement may comprisea control surface and may take the form of any of the following options:

[0009] 1. A trailing edge flap in one or more spanwise sections of thewinglet.

[0010] 2. A leading edge flap in one or more spanwise sections of thewinglet.

[0011] 3. A leading edge upper surface trip device which may deploy fromwithin the winglet envelope so as to cause air flow over the uppersurface to separate and thereby reduce lift.

[0012] 4. At least one passage formed in the winglet which extends fromthe bottom surface to the top surface of the winglet and which can beopened to allow high pressure air at the lower surface to flow upwardlytherethrough to the upper surface to reduce lift. The passage maynormally be closed by a member which preferably serves as a spoiler whenthe member is moved to open the passage. Preferably, two such membersare provided for closing the passage at the upper and lower surfaces ofthe winglet.

[0013] When the aircraft undergoes a high g manoeuvre, for example 2.5g,the control arrangement on the winglet may be operable to reduce thelift that it would otherwise generate.

[0014] In the passive control case, the control arrangement may compriseany of the following options:

[0015] 1. A movable, for example, deformable leading edge which willmove in an appropriate sense under a predetermined load to reduce lift.

[0016] 2. A movable, for example, deformable trailing edge which willmove in an appropriate sense under a predetermined load to reduce lift.

[0017] 3. At least one passage formed in the winglet which extends fromthe bottom surface to the top surface of the winglet and which is openedby means such as a louvre arrangement at a predetermined load to allowhigh pressure air at the lower surface to flow upwardly through thepassage to the upper surface to reduce lift.

[0018] 4. A winglet section designed such that the flow breaks down,i.e. separates at a predetermined load condition.

[0019] According to a second aspect of the invention there is provided amanoeuvre load alleviation system which includes a winglet according tothe first aspect of the invention or any of the subsidiary clausesrelating thereto

[0020] According to a third aspect of the invention there is provided anaircraft wing having winglet according to the first aspect of theinvention or any of the subsidiary clauses relating thereto.

[0021] According to a fourth aspect of the invention there is providedan aircraft having a wing according to the third aspect of theinvention.

[0022] A winglet in accordance with the invention will now be describedby way of example with reference to the accompanying drawings in which:

[0023]FIG. 1 is a perspective view of a known form of winglet at the tipof an aircraft wing,

[0024]FIG. 2 is a diagrammatic front view of part of an aircraftillustrating the way in which lift at the winglet creates a bendingmoment at the wing root.

[0025]FIG. 3 is a graph showing the way in which the addition of awinglet increases the loading on an aircraft wing, and hence the wingbending moment,

[0026]FIG. 4 is a perspective view similar to FIG. 1 showing a wingletin accordance with the present invention; and

[0027] FIGS. 5 to 11 are cross-sections taking chordwise through thewinglet of FIG. 4 showing various types of airflow control arrangementson the winglet by means of which lift generated by the winglets can bevaried.

[0028] Referring to FIGS. 1 to 3, a wing 10 of an aircraft 11 has aknown type of winglet 12 which takes the form of an upturned tip at theouter end of the wing 10. The winglet 12 serves to increase theefficiency of the wing 10 by reducing drag which would otherwise beinduced by wing tip vortices during flight.

[0029] The winglet 12 generates lift in its own right and, as shown inFIG. 2, the lift at the winglet 12 generates an inwardly directed force14 which creates a bending moment about a root 16 of the wing 10 throughan effective moment arm 18. The presence of the winglet 12 alsoincreases the loading on the wing 10 as shown in FIG. 3 and creates anadditional bending movement about the wing root. In FIG. 3, axis xrepresents semi-span of the wing and axis y represents spanwise loading.A curve indicated at A indicates the typical loading of a wing which isnot provided with a winglet. The additional curve B represents theadditional load on the wing due to the presence of the winglet.

[0030] In general, large areas of aircraft wings are designed either byloads generated during a manoeuvre (eg a 2.5 g pull-up) or by fatigueloads, i.e. cyclic loading by uploads in 1 g flight and downloads whenthe aircraft is on the ground.

[0031] The additional of a winglet 12 increases the loads in both ofthose cases and the winglet of the present invention has as an object tomaintain drag savings whilst minimising the additional loads generatedby the winglet when the aircraft is in flight. To achieve that object,the present invention provides an airflow control arrangement on thewinglet which is primarily intended to reduce the lift generated by thewinglet during manoeuvres. Various control arrangements are shown inFIGS. 5 to 11 and will now be described.

[0032] As shown in FIGS. 4 and 5, a trailing edge flap 20 may beprovided in one or more spanwise sections of the winglet 12 (a singlesection only being shown) and is linked to the normal manoeuvre loadalleviation system 22 of the aircraft. During a manoeuvre, the trailingedge flap 20 can be raised as shown in FIG. 5 to reduce the lift on thewinglet 12.

[0033]FIG. 6 is a view similar to FIG. 5 but showing a different type oftrailing edge device (a spoiler) 24 which can be moved upwardly from aposition flush with an upper surface 26 of the winglet 12 to reducelift. One or more spoilers 24 can be provided in one or more spanwisesections of the winglet 12. The lower surface (indicated at 27) of thewinglet 12 remains unaffected by movement of the spoiler 24.

[0034] Looking at FIG. 7, a leading edge flap 28 is provided, againlinked to the manoeuvre load alleviation system 22 of the aircraft toreduce lift. Flaps 28 can be provided in a plurality of leading edgesections.

[0035] In FIG. 8, an alternative type of leading edge flap 30 isprovided in the upper surface of a leading edge section 31 of the wing10. The flap 30 is movable from a position flush with the leading edgesection 31 to the raised position to reduce lift by causing the uppersurface flow to separate. Again, flap 30 can be provided in a pluralityof leading edge sections.

[0036] In FIG. 9, a trip device 32 is arranged in one or more leadingedge sections 31 and can be deployed from within the winglet envelope soas to project above the upper surface 26 of the winglet. The trip device32 comprises an elongate plate 36 or series of plates which may or maynot be continuous along the winglet span which is moveable in a suitableguide arrangement 38 in the leading edge section 31. On lifting theplate 36 into the position shown in FIG. 9, the flow over the uppersurface 26 of the winglet 12 separates downstream of the plate 36thereby reducing lift on the winglet 12.

[0037] Looking at FIG. 10, a passage 40 is formed in the winglet 12 soas to extend from the lower surface 27 through to the upper surface 26.The passage 40 is openable and closeable by means of upper and lowerdoors 42, 46 respectively. The door 42 is hinged to the winglet 12 atthe forward edge of the passage 40 and the lower door 46 is hinged atthe aft edge of the passage 40. The passage 40 extends spanwise alongthe winglet 12 and, if desired, a plurality of passages may be arrangedin respective spanwise sections. With the aircraft in normal levelflight, both of the doors 42, 46 lie flush with the respective upper andlower surfaces 26, 27 of the winglet 12. Where a reduction in wingletlift is required, the doors 42, 46 are opened, for example by means ofthe manoeuvre load alleviation system 22 of the aircraft so as to venthigh-pressure air from the lower surface 27 to the upper surface 26through the passage 40 and thereby reduce lift. The positioning of thedoor 46 as shown in FIG. 10 encourages a flow of air into the passage 40and the upper door 42 acts as a spoiler to cause flow separation overthe downstream section of the upper surface 26.

[0038] In FIG. 11, a passage 50 is formed in the winglet 12 so as toextend from the lower surface 27 to the upper surface 26. A plurality ofdoors in the form of pivoted louvres 52 are provided for opening andclosing the upper end of the passage 50 and a similar series of pivotedlouvres 54 is provided for opening and closing the lower end of thepassage 50. In the previous embodiments, the air flow controlarrangements are preferably operated by means of the manoeuvre loadalleviation system of the aircraft. Whilst the louvres 52, 54 in FIG. 11could be operated in that way, at a certain critical pressure, forexample, when approaching the load limit of a particular manoeuvre, thelouvres 52, 54 will be forced open by the air so as to vent highpressure air from the lower surface 27 to the upper surface 26 throughthe passage 50 thereby reducing lift. In the normal cruise conditionthese louvres 52, 54 lie flush with the winglet surfaces 26, 27respectively.

[0039] The arrangement shown in FIGS. 5 to 10 could be regarded as“active” control arrangements whereas the embodiment shown in FIG. 11could be regarded as a “passive” control arrangement adapted to operateautomatically at a given pressure. If desired, one or more of the otherembodiments could be arranged to deform or deflect somewhat as shown inFIG. 8 at a critical pressure. If desired, the winglet 12 may have atrailing edge section arranged to deform or defect at a criticalpressure to reduce lift.

[0040] It will be appreciated that the reduction in lift which can beachieved with a winglet in accordance with the invention will reduce theoverall lift generated by the wing 10. Whilst the reduction in liftgenerated by the winglet 12 reduces the bending moment illustrated inFIGS. 2 and 3 particularly during in-flight manoeuvres, the loss of liftat the winglet 12 may need to be compensated for by increasing the angleof incidence of the wing 10. However, such an increase to compensate forthe loss at the winglet 12 provides a nett effect whereby the sameoverall lift will be generated but further inboard along the wing thanin the case when the winglet load alleviation system is not activatedand hence the overall bending moment on the wing will be reduced

[0041] Where an activated control surface is provided on the winglet, itmay be possible to use the control surface for any of the followingpurposes:

[0042] to help control the wing tip vortex behaviour of the aircraft andhence help minimise the wake vortex characteristics;

[0043] to generate extra lift and/or reduce drag for certain phases offlight (e.g. take-off);

[0044] to provide additional yaw control;

[0045] to provide an air-braking function;

[0046] to help control wing tip stall;

[0047] to optimise flying surface geometry/drag in cruise

1. A winglet for an aircraft wing, the winglet having an air flowcontrol arrangement thereon by means of which lift generated by thewinglet can be varied.
 2. A winglet according to claim 1 in which theair flow control arrangement is a control surface.
 3. A wingletaccording to claim 1 or 2 in which the air flow control arrangement isan active control arrangement linked to a control system of the aircraftsuch as a manoeuvre load alleviation system.
 4. A winglet according toclaim 2 in which the control surface comprises a trailing edge flap inone or more spanwise sections of the winglet.
 5. A winglet according toclaim 1, 2 or 3 in which the control arrangement comprises a leadingedge flap in one or more spanwise sections of the winglet.
 6. A wingletaccording to claim 2 or 3 in which the control arrangement comprises adevice on a leading edge upper surface which is arranged to cause airflow over an upper surface of the wing to separate to reduce lift.
 7. Awinglet according to claim 6 in which the device is housed within anenvelope of the winglet and is movable into position above the leadingedge upper surface to cause the air flow to separate.
 8. A wingletaccording to claim 1 or 2 in which the control arrangement comprises atleast one passage formed in the winglet which extends from a lowersurface thereof to an upper surface thereof and which can be opened toallow high pressure air at the lower surface to flow upwardlytherethrough to the upper surface to reduce lift.
 9. A winglet accordingto claim 8 in which the passage is normally closed by at least onemember which serves as a spoiler when the member is moved to open thepassage.
 10. A winglet according to claim 9 in which one such member isprovided for closing the passage at each of the upper and lower surfacesof the winglet.
 11. A winglet according to claim 1 or 2 in which thecontrol arrangement is a passive control arrangement operable inresponse to a predetermined condition.
 12. A winglet according to claim11 when dependent on claim 2 in which the control surface comprises amovable leading edge or leading edge section which will move in responseto the predetermined condition.
 13. A winglet according to claim 12 inwhich the movement of the control surface is effected by deformation ofthe leading edge or leading edge section.
 14. A winglet according toclaim 11 when dependent on claim 2 in which the control surfacecomprises a movable trailing edge or trailing edge section arranged tomove in response to the predetermined condition.
 15. A winglet accordingto claim 14 in which the movement of the control surface is effected bydeformation of the trailing edge or trailing edge section.
 16. A wingletaccording to claim 11 in which the control arrangement comprises apassage formed in the winglet which extends from a lower surface thereofto an upper surface thereof and which is openable in response to thepredetermined condition to allow high pressure air at the lower surfaceto flow upwardly through the passage to the upper surface to reducelift.
 17. A winglet according to claim 16 in which the passage isopenable and closeable by means of a cover arrangement at one of theupper and lower surface of the winglet.
 18. A winglet according to claim17 in which the cover arrangement comprises a louvre arrangement.
 19. Awinglet constructed and arranged substantially as described herein withreference to the accompanying drawings.
 20. A manoeuvre load alleviationsystem for an aircraft which includes a winglet according to anypreceding claim.
 21. An aircraft wing having thereon a winglet accordingto any of claims 1 to
 19. 22. An aircraft wing constructed and arrangedsubstantially as described herein with reference to the accompanyingdrawings.
 23. An aircraft having a wing according to claim 21 or 22.